Researchers examined data for 1985-8 and for those still alive in 1992-3.

Once adjustments were made for factors such as age, smoking and illness, the study was able to isolate the effect of changes in sleep patterns.

The average night’s sleep is seven hours but around a third of adults in Britain regularly sleep five hours or fewer a night.

Professor Francesco Cappuccio, of the University of Warwick medical school, said: “Fewer hours of sleep and greater levels of sleep disturbance have become widespread in industrialised societies.

“This change, largely the result of sleep curtailment to create more time for leisure and shiftwork, has meant that reports of fatigue, tiredness and excessive daytime sleepiness are more common. Sleep represents the daily process of physiological restitution and recovery, and lack of sleep has far-reaching effects.

“Our findings indicate that consistently sleeping around seven hours per night is optimal for health.”

He said insufficient sleep was a risk factor in weight gain, high blood pressure and type 2 diabetes.

But it is unclear how sleeping too long could cause ill-health, he added, although possible causes included depression and low socio-economic status.

Last week, researchers showed that children who did not get enough sleep were more likely to become obese as adults.